The present invention relates generally to a Pierce-type electron gun, and, more particularly, to a system and method for controlling operation of a Pierce-type electron gun to control current density in the electron beam and control the operating temperature of the electron emitter and the filament, so as to keep the temperature of both the electron emitter and the filament to their lowest possible operating temperature.
X-ray tubes typically include a cathode structure that provides an electron beam that is accelerated using a high voltage applied across a cathode-to-anode vacuum gap to produce x-rays upon impact with a rotating anode. The area where the electron beam impacts the anode is often referred to as the focal spot. Typically, the cathode includes one or more cylindrical or flat filaments positioned within a cup for providing electron beams to create a high-power large focal spot or a high-resolution small focal spot, as examples. Imaging applications may be designed that include selecting either a small or a large focal spot having a particular shape, depending on the application.
One specified cathode structure for generating the electron beam is a Pierce-type electron gun. The Pierce-type electron gun includes a heating filament, an electron emissive cathode, field shaping electrodes and a first extraction plate spaced from the cathode, and an X-ray target anode spaced from the extraction plate. A particular embodiment of such a Pierce gun is disclosed in U.S. Pat. No. 3,882,339. Such electron guns are typically operated in space charge limited regime and the emission current can be readily controlled by adjusting the extraction voltage. Such a gun would be particularly suited to produce electron beams with rapidly variable amperage.
One drawback to existing Pierce-type electron guns is the control of voltage, and the control and limitation of the power needed to keep the emitter and filament at the proper operating temperatures. In order to extend the life of the components, the various temperatures need to be as small as possible compatibly with the proper operation. Additionally, the control needs to be done with the least number of feedback lines possible and these lines should not come from inside the vacuum chamber, and additional equipment inside the chamber (e.g., to measure temperature) should be avoided.
Thus, a need exists for a system and method that allows for control of electron beam intensity in a very fast fashion by quick application of a voltage generated by a voltage supply. It would also be desirable to have a system that allows for controlling the temperature of the emitter in a fast and accurate fashion while minimizing the operating temperature of both the filament and the emitter.